The present invention is a technique relating to a method of manufacturing a semiconductor device utilizing a crystalline semiconductor thin film containing silicon as a main component. More particularly, the invention relates a method of manufacturing a thin film transistor (hereinafter, referred to as TFT) utilizing a substrate having a crystalline semiconductor thin film containing silicon as the main component on an insulating substrate.
Throughout the present specification, the semiconductor device generally designates a device which functions utilizing a semiconductor. Thus, the electronic device or the like mounted thereto such as an arithmetic processing device, a storage processing device, or an electro-optical device as well as a single element such as the TFT are all contained in the category of the semiconductor device.
An active matrix liquid crystal display device is a monolithic display device in which a pixel matrix circuit and a driver circuit are provided on the same substrate. In the monolithic display device, it is the main stream, to employ the thin film transistors (TFTs). In the thin film transistor, an amorphous silicon film is formed on an insulating substrate such as a glass substrate or a quartz substrate to obtain an active layer. The development of a system-on-panel incorporating therein logic circuits such as a memory circuit and a clock generating circuit utilizing the TFTs has been advancing.
The high speed operation is required for such a driver circuit and the logic circuit, and therefore it is not suitable therefor that the amorphous silicon film is formed as the active layer on the quartz substrate or the glass substrate to obtain an element. For this reason, at present TFT in which a polycrystalline silicon film is used as the active layer is manufactured.
There are present some technologies in which after having deposited the amorphous silicon film on the quartz substrate or the glass substrate, the polycrystalline silicon film is obtained through crystallization. Of those, there is known a technique in which the catalytic metal element, with which the excellent electrical characteristics of the element are obtained when forming the element, and which promotes the crystallization of the amorphous silicon film, is added to the film to conduct the crystallization by a heat treatment. This technique will hereinbelow be described in more detail.
A semiconductor thin film having the amorphous structure containing as a main component a silicon is formed on an insulating substrate such as a quartz substrate or a glass substrate into a thickness on the order of 50 nm to 100 nm by LPCVD or the PECVD. Metal is added to the surface of the semiconductor thin film or into the semiconductor thin film having the above-mentioned amorphous structure to carry out the heat treatment therefor, thereby crystallizing the semiconductor thin film having the above-mentioned amorphous structure in the solid phase. The semiconductor thin film having the above-mentioned amorphous structure is crystallized in the solid phase so that a crystalline semiconductor thin film containing silicon as the main component is formed. Then, it is confirmed by the inventors of the present invention that the addition of the metal promotes the solid-phase crystallization, and it is therefore said that the metal acts as the catalyst during the solid-phase crystallization. In the present specification, the metal is referred to as the catalytic metal.
As for the phenomenon that the semiconductor thin film having the above-mentioned amorphous structure is crystallized by the heat treatment with the metal as a catalyst, a large number of reports have been made as the Metal Induced Lateral Crystallization (MILC). As the typical ones, there are the transition metal elements such as nickel (Ni), cobalt (Co), palladium (Pd), platinum (Pt), and copper (Cu). The presence of the catalytic metal becomes advantageous in the temperature and the time required for the semiconductor thin film having the above-mentioned amorphous structure to be crystallized in the solid phase as compared with the case where no catalytic metal is added. As a result, it has become clear that the Ni element shows excellent property as the catalytic metal. Hereinbelow, descriptions will be made on the assumption that the Ni element is employed as the catalytic metal.
The heat treatment required for the solid phase crystallization of the semiconductor thin film having the above-mentioned amorphous structure is performed at from 400xc2x0 C. to 700xc2x0 C. for several hours or more by the electric furnace, etc.
In the present specification, the semiconductor thin film having the amorphous structure containing silicon as the main component includes a SiGe thin film having the amorphous structure, in which the component ratio of Ge is less than 50%.
For the catalytic metal for promoting the crystallization of the semiconductor thin film having the above-mentioned amorphous structure, the transition metal element such as nickel (Ni), cobalt (Co), palladium (Pd), platinum (Pt), or copper (Cu) is employed. As generally well known, the metal such as Ni, if it is present in crystalline silicon, forms the deep levels to have a bad influence on the electrical characteristics and the reliability of the element. Therefore, the metal such as a Ni element needs to be removed from the region (element active region) in which the element is formed, and is used as the element. The above-mentioned crystalline semiconductor thin film is also concerned about the bad influence exerted on the element characteristics due to the catalytic metal.
Therefore, the metal such as the Ni element needs to be removed from the element active region to the degree at which it does not have a bad influence on the electrical characteristics. Removing the metal such as the Ni element from the element active region in the crystalline silicon is generally called gettering. The method of gettering which has been confirmed by the inventors of the present invention will hereinbelow be described.
An insulating film is formed on the above-mentioned crystalline semiconductor thin film. The insulating film is formed using a silicon oxide film, a silicon nitride film, or the like by the CVD apparatus or a sputtering apparatus. Then, the insulating film is formed into island-like shape. The island-like structure of the insulating film can be formed by utilizing photolithography and etching, which are general in the semiconductor technology.
A nonmetal element or ion of the nonmetal element is added to the crystalline semiconductor thin film with the insulating film as a mask, and a region, to which the nonmetal element or the ion of the nonmetal element has been added, is formed on the crystalline semiconductor thin film. That is, the nonmetal element or the ion of the nonmetal element is not added to the region in which the island-like structure of the insulating film is present on the crystalline semiconductor thin film, but are added to the region in which the island-like structure of the insulating film is absent. The nonmetal element or the ion of the nonmetal element is added thereto by thermal diffusion from a gas phase or by utilizing an ion implantation apparatus.
The nonmetal element or the ion of the nonmetal element is one kind of or plural kinds selected from the group consisting of boron (B), silicon (Si), phosphorus (P), arsenic (As), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).
The mechanism and the phenomenon of gettering of the transition metal elements in monocrystalline silicon are actively studied, and as a result, a considerable part thereof has become clear. While some of gettering in the polycrystalline silicon does not become clear in detail, the case of the monocrystalline silicon may be referred therefor. In polycrystalline silicon as well, the damage which is caused by the ion implantation method becomes an effective gettering. The mark which is generated by knocking over the atoms by the ion implantation becomes locally amorphous, and when recrystallizing the amorphous part by the subsequent heat treatment, the crystal defects etc. are generated with high density. Therefore, any of the nonmetal elements or ions of the nonmetal elements which are added thereto by the ion implantation during gettering is available as long as the ion implantation is possible therefor, it is hardly diffused up to the element active region even by the heat treatment because the diffusion coefficient thereof is smaller than that of the metal gettered, and it has no influence on the element characteristics because it is electrically inactive.
As for the elements satisfying the above-mentioned conditions, there are one kind or plural kinds of elements selected from the group consisting of B, Si, P, As, He, Ne, Ar, Kr, and Xe. However, it is conceivable that the situation of generation of the damages such as the grain boundaries, the micro-twins, the stacking faults, the dislocation loops, and the dislocation networks differ depending on the difference in the ion kind, the dose, the acceleration energy and the like. In addition, if phosphorus (P) or the like, even when diffused from the gas phase, is added to crystalline silicon, then misfit transition is formed to become the gettering source. It is confirmed by the present inventors that adding phosphorus (P) to the above-mentioned crystalline semiconductor thin film is effective to gettering of the above-mentioned catalytic metal.
Next, the crystalline semiconductor thin film is subjected to the heat treatment at the temperature equal to or higher than 400xc2x0 C. and equal to or lower than 1,000xc2x0 C. so that the metal is gettered to the region to which the nonmetal element or the ions of the nonmetal element has(have) been added. It is confirmed on the basis of the experiment by the inventors of the present invention so that in particular, phosphorus (P) has a remarkable gettering effect.
Generally, gettering forms the site for gettering outside the element active region, and the metal is segregated to the gettering site by the heat treatment. While in the technique of forming semiconductor element including the formation of the above-mentioned thin film, the heat treatment is essential thereto, and it is desirable that, the heat supply amount=the temperaturexc3x97the time, is small as much as possible. If the heat supply amount is reduced, then this becomes economically advantageous so that the time can be shortened. In addition thereto, the warp or the contraction of the semiconductor substrate can be reduced, and also the generation of such as the excessive stress in the vicinity of the element active region can be prevented. In addition, the less the residual metal is, which can not be gettered in the element active region after the completion of the gettering process, the better it is.
A semiconductor thin film 10102 having the amorphous structure containing silicon as the main component is formed on a glass substrate or a quartz substrate 10101. Metal is then added to the semiconductor thin film 102 having the amorphous structure. While as for the above-mentioned metal, there are conceivable nickel (Ni), cobalt (Co), palladium (Pd), platinum (Pt), copper (Cu) or the like, Ni is employed in the item of means for solving the problem, and also Ni acetate solution 10103 is applied thereto.
The semiconductor thin film 10102 having the amorphous structure is crystallized in solid phase with the metal as the catalyst by the heat treatment at the temperature equal to or higher than 400xc2x0 C. and equal to or lower than 700xc2x0 C. to obtain a crystalline semiconductor thin film containing silicon as the main component (refer to FIG. 1A). It is confirmed on the basis of the experiment by the inventors of the present invention that Ni is a metal effective in promoting the solid-phase crystallization.
After an insulating film has been deposited on a crystalline semiconductor thin film 10107, the insulating film is fine-patterned into an island-like structure 10104. Then, nonmetal element or ions of the nonmetal element is(are) added to the crystalline semiconductor thin film with the island-like structure 10104 of the insulating film as a mask (refer to FIG. 1B). It is assumed that phosphorus (P) is employed as the nonmetal element in the item of means for solving the problem.
It is conceivable that in addition to phosphorus (P), B, Si, As, He, Ne, Ar, Kr, Xe or the like is effective for gettering. Each of these elements is the element which can introduce the damage to a poly-Si film by the ion implantation and the subsequent heat treatment, which is more hard to diffuse than the metal to be gettered, or which is inactive and hence does not have an influence on the element characteristics.
Regions 10106 and 10109 to which the nonmetal element or the ions of the nonmetal element has(have) been added are formed on the crystalline semiconductor thin film. The crystalline semiconductor thin film is subjected to the heat treatment at the temperature equal to or higher than 400xc2x0 C. and equal to or lower than 1,000xc2x0 C. to getter the metal to the region to which the nonmetal element or the ions of the nonmetal element has(have) been added (refer to FIG. 1C). In FIG. 1C, reference numeral 10110 designates the direction of the movement of Ni.
One of the features of the present invention resides in that it has the process of adding nonmetal element or ions of the nonmetal element to a crystalline semiconductor thin film to form the gettering site and the process of carrying out the heat treatment, so that the metal contained in a crystalline semiconductor thin film is moved by the heat treatment to be captured in the gettering site (the region to which the nonmetal element or the ions of the nonmetal element has(have) been added), and as a result the metal is removed or reduced from the crystalline semiconductor thin film other than in the gettering site.
The main constitution of the present invention is that the island-like insulating film shapes 10301 and 10201 for the surface parallel with a surface 10203 of the crystalline semiconductor thin film 10206 are polygons having n (n greater than 20) vertexes and also a polygon having m (m greater than 8) vertexes, in which the interior angle is equal to or larger than 180xc2x0 C., of these vertexes.
From the foregoing, the area of a boundary surface 10108 between the region 10106 and 10109 to which the nonmetal element or the ions of the nonmetal element has(have) been added and the region to which the nonmetal element or the ions of the nonmetal element has(have) not been added is increased to improve at least one of the efficiency and the effect of gettering.
In general, the progress of gettering includes the steps of releasing the metal from the element active region, the diffusion step and the step of capturing the metal in the gettering site. The area of the boundary surface therebetween is increased, the phenomenon of diffusing the metal is promoted, and so forth, to thereby aim at enhancing the efficiency or the effect of gettering.